The present invention relates to voice coil motors (VCM) in disc storage systems. In particular, the present invention relates to an adaptive pulse-shaping method for unlatching a VCM in a disc storage system.
In disc drives, a VCM is used to position the transducer heads over a desired radial position on a stack of discs that store information. When the disc drive is energized and the discs are spinning, the VCM positions the heads over data stored on the spinning discs. When the disc drive is de-energized, the discs stop spinning, and the heads with the VCM are moved to a xe2x80x9cparkxe2x80x9d position of the discs. Typically, no data is stored on the park position. Various kinds of latches are used to latch the VCM in the park position when the disc drive is de-energized. A latching mechanism can be a magnetic latch or any other form of mechanical latch.
Unlatching the VCM is one of the first tasks for the disc drive under a cold start condition. In this condition, the latch force may be a combination of the designed latch force of the latching mechanism, the force associated with sticking friction (xe2x80x9cstictionxe2x80x9d) between the heads and the disc, a bias force applied by a flexible head suspension, etc. These forces vary from one drive to another. Further, the VCM actuator system parameters such as the VCM torque constant, Kt, can be changed among the drives and as the drive operational environment changes. The latch force can even vary between each unlatch operation because of variations in stiction. In spite of these variations, unlatch operations must always be smooth to prevent damage to the disc and to help ensure proper read/write operations.
One technique for unlatching a VCM is to apply an open loop kick-off current pulse. However, since the latch force can vary widely, applying the same open loop kick-off current pulse for each unlatch operation will not result in a smooth transfer from open loop control to the feedback control. Also, excessive head velocity overshoot may occur, resulting in the head colliding with the disc medium if the kick-off current pulse method is used in a ramp load drive.
Another unlatch technique is described in U.S. Pat. No. 5,600,219 entitled xe2x80x9cSENSORLESS CLOSED-LOOP ACTUATOR UNLATCHxe2x80x9d. This unlatch scheme deals with adjusting unlatch current amplitude incrementally, followed by the application a negative current pulse to decelerate the VCM as soon as the unlatch is confirmed. This system does not take into consideration the possibility of varying the width of unlatch current pulses to optimize the unlatch process. Further, final pulse width and amplitude values of a final unlatch current pulse from a previous unlatch operation are not stored for reference in the next unlatch operation. Thus, this unlatch technique does not guarantee a smooth unlatch process.
The present invention addresses these problems, and offers other advantages over the prior art.
The present embodiments relate to disc storage systems that employ an adaptive pulse-shaping scheme for unlatching a VCM in a disc drive, thereby addressing the above-mentioned problems.
One embodiment relates to a method for unlatching a VCM in a disc drive. The method includes determining if the VCM is stationary and applying a first unlatch current pulse that has a first amplitude and first width to the VCM if the VCM is found to be stationary. An incremented unlatch current pulse is then applied to the VCM if the VCM is found to be stationary after application of the first unlatch current pulse. The incremented unlatch current pulse has at least one of an amplitude and a width that is greater than at least one of the corresponding first amplitude and the first width of the first unlatch current pulse.
Another embodiment relates to a disc storage system that includes a VCM velocity control loop operating a VCM and an adaptive current pulse shaping means coupled to the VCM velocity control loop. The adaptive current pulse shaping means is capable of providing unlatch current pulse for unlatching the VCM.